Potentiometer based controller for oven

ABSTRACT

A temperature control system for controlling an oven temperature comprises a potentiometer and a processor. The potentiometer comprises a shaft and at least a first and a second terminal, and provides a variable resistance between the first terminal and the second terminal in response to a rotation of the shaft. The variable resistance forms a resistance output value. The processor is configured to detect one of a plurality of set point modes each comprising a different number of non-sequential temperature set points each of which span a range of resistances of the potentiometer, and convert the output resistance of the potentiometer into a temperature setting signal that corresponds with a temperature assigned to the resistance range of the measured resistance output.

CROSS-REFERENCE TO RELATED APPLICATION

The present patent document claims the benefit of the filing date under 35 U.S.C. § 119(e) of Provisional U.S. Patent Application Ser. No. 62/454,527, filed Feb. 3, 2017, which is hereby incorporated by reference.

TECHNICAL FIELD

The subject disclosure is directed to a controller for an oven, and more particularly to a temperature control system for controlling an oven temperature.

BACKGROUND INFORMATION

Ovens are well known appliances that are useful for drying, heating, and cooking products. Some ovens are used for industrial application purposes, while other ovens are used for food preparation purposes. Often, it is desirous for the oven to be brought to a specific temperature so that an item placed within an oven cavity may be dried, heated, or cooked. Many ovens include an adjustable temperature control, such as a knob, that allows a user to rotate the knob to select the temperature at which the oven should operate. However, the temperature control on some of these ovens operates in direct correlation to the amount that the temperature control knob is rotated. Too much rotation of the temperature control knob and the temperature setting will pass the desired temperature resulting in too hot of an oven. Too little rotation of the temperature control knob and the desired temperature setting is not reached, resulting in an oven that is too cold.

BRIEF SUMMARY

A temperature control system for controlling an oven temperature comprises a potentiometer and a processor. The potentiometer comprises a shaft and at least a first and a second terminal, and provides a variable resistance between the first terminal and the second terminal in response to a rotation of the shaft. The variable resistance forms a resistance output value. The processor is configured to detect one of a plurality of set point modes each comprising a different number of non-sequential temperature set points each of which span a range of resistances of the potentiometer, and convert the output resistance of the potentiometer into a temperature setting signal that corresponds with a temperature assigned to the resistance range of the measured resistance output.

Other systems, methods, features, and advantages of the invention will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the invention, and be protected by the following claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principals of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views.

FIG. 1 is a partial schematic of a first exemplary oven heating circuit with an enhanced portion of the circuit.

FIG. 2 is an illustration of a potentiometer.

FIG. 3 is a flow diagram for assigning a temperature to a range of resistances along portions of the potentiometer.

FIG. 4 is an illustration of 3 set point regions along the resistive portions of a potentiometer.

FIG. 5 is an illustration of 5 set point regions along the resistive portions of a potentiometer.

FIG. 6 is an illustration of 8 set point regions along the resistive portions of a potentiometer.

FIG. 7 is an illustration of a 3 set point mode highlighting an active region.

FIG. 8 is a partial schematic of a second exemplary oven heating circuit with an enhanced portion of the circuit.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERRED EMBODIMENTS

A temperature control system improves the selectability of an oven temperature. The system uses a continuous device to generate non-sequential discrete temperature signals to control the temperature within an oven cavity. Thus, rather than the oven's temperature signal being directly proportional to the amount of rotation of the continuous device, the temperature control system selects from one of a plurality of different set point modes, where each mode has a different number of regions spaced around the rotational movement of the continuous device, and where each region is assigned different predetermined temperatures. Analysis of the resistance measured across terminals of the continuous device correlates to a specific region and predetermined temperature setting from the selected set point mode for controlling the oven's temperature. Advantageously, the temperature control system allows a user to select an oven temperature without concern that a temperature control knob must be turned to an exact location for the oven to reach a desired temperature. The system may also eliminate the need for manufacturers to purchase multiple different mechanical thermostat switches for use with various configurations of ovens.

FIG. 1 is a partial schematic of an oven heating circuit 100 that shows the general components and wiring of a gas convection oven using a temperature control system. Also shown in FIG. 1 is an enhanced portion of the circuit. An operation selector switch 102 may control the operation of the oven. As illustrated in FIG. 1, the operation selector switch 102 is a multimode switch that can be used to turn the oven heating circuit 100 OFF or ON in various modes of operation. In some ON configurations, the oven heating circuit 100 activates a heating element and a blower motor to circulate heated air throughout the oven cavity to a set temperature. In other ON configurations, the oven heating circuit 100 can activate the blower motor without activating the heating element to operate in a cool down mode. While FIG. 1 illustrates a multimode operation selector switch 102, the heating circuit 100 could alternatively be configured with one or more single mode switches that can each control a different heating and/or circulation function of the oven.

When the operation selector switch 102 is turned ON and set to a cooking mode, a power source supplies power to the oven heating circuit 100 through power lines L1 and N that can in turn provide power to a blower motor 104, a cooling fan 106 and a transformer 108. A door switch 110 may be included as a safety function to ensure that the blower motor 104 does not operate during a cooking mode when the oven door is open.

The transformer 108 provides a stepped down power from that received on power lines L1 and N to a spark ignition control 112. In FIG. 1, the spark ignition control 112 is used to generate a flame for converting a gaseous fuel to heat that is then circulated throughout a cavity of the oven by the blower motor 104. The gaseous fuel may be supplied through a gas line, and may be either natural gas or liquefied petroleum gas.

The processor 114 may evaluate a number of paired input pins on the processor 114 to determine if any are shunted together. Based on the determination of which of the paired input pins are shunted together, the processor 114 selects from the plurality of set point modes which mode, and therefore the number of different assignable temperature regions and each region's predetermine temperature, is active during a cooking mode.

Alternatively, processor 114 may access a set point mode parameter retained in a memory. The set point mode parameter may define which of the plurality of set point modes should be used by the processor when the oven heating circuit 100 is active during a cooking mode.

A continuous device, such as a potentiometer 116, may be in communication with processor 114. The potentiometer 116 may operate as a temperature selection device for the oven heating circuit 100 with each of a first terminal 202, a second terminal 204, and a third terminal 206 of the potentiometer 116 connected to terminals of the processor 114. A knob may be placed at the end of the potentiometer's 116 shaft 208 so that a user can rotate the shaft 208. As a shaft 208 of the potentiometer 114 is rotated, a wiper within potentiometer 116 sweeps across a conductive strip and resistive strip of the potentiometer 116 thereby varying the resistance over which the wiper has traversed. An indicator may be included on a face of the knob that correlates with the location of the potentiometer's 116 wiper. This indicator allows the user to identify an amount of rotation of the knob and the location where on the rotational path of the potentiometer 116 the wiper is located.

The potentiometer's 116 resistance as a result of the rotation of its wiper may be measured by the processor 114 across a first terminal and second terminal of the potentiometer 116. This output resistance of the potentiometer 116 is directly proportional to the distance moved by the wiper of the potentiometer 116, such that the output resistance of the potentiometer 116 is a percentage of the total resistance of the potentiometer 116, and may be correlated with a set point mode region, as explained in conjunction with FIG. 2.

The processor 114 may also receive from a probe 118 positioned within the oven cavity an input signal that varies with the temperature in the oven cavity. In some ovens, this probe 118 may be a resistance temperature detector. The processor 114 may evaluate the probe 118 signal and determine the temperature within the oven cavity. Based on the temperature sensed from the probe 118 and a desired temperature setting determined from the region correlating with the resistive output of potentiometer 116, the processor 114 may output a control signal to spark ignition control 112 to increase or decrease the temperature within the oven until the processor 114 determines based on measurements from probe 118 that the desired temperature has been achieved.

Referring to FIGS. 1-6, at step 302 an oven operation mode switch 102 is engaged to a cooking position. At step 304, the processor 114 evaluates the set point mode in which the system is configured to operate. In some systems, the processor 114 may access a set point mode parameter retained in a memory. The memory may be internal to the processor 114 or may be external to the processor 114 and in communication with it. The set point mode parameter may define which of the plurality of set point modes should be used by the processor 114 when the oven heating circuit 100 is active during a cooking mode. In other systems, the processor 114 may evaluate processor configuration pins to determine which pair of pins are shunted together to identify which set point mode to select from a plurality of set point modes retained in the memory associated with the processor 114. For example, in some oven heating circuits 100 that utilize a shunt to configure the set point mode, a processor 114 may include five pin pairs that are used to determine the set point mode. Shunting the first pair of processor pins together may cause the processor 114 to interpret the output resistance of the potentiometer 116 as a standard continuous device. Shunting the second pair of processor pins together may cause the processor 114 to divide the full resistance of the potentiometer 116 into a first number of regions, such as three equally sized regions as illustrated in FIG. 4. Shunting the third pair of processor pins together may cause the processor 114 to divide the full resistance of the potentiometer 116 into a second number of regions, such as five equally sized regions as illustrated in FIG. 5. Furthermore, shunting the forth pair of processor pins together may cause the processor 114 to divide the full resistance of the potentiometer 116 into third number of regions, such as eight equally sized regions as illustrated in FIG. 6. Thus, changing which pair of processor pins are shunted together changes the number of set point regions and thus the number of temperatures that may be selected with the potentiometer. An exemplary temperature setting table, that may be retained in the memory associated with processor 114, illustrates how different predetermined temperatures can be assigned to the different set point regions:

Position 3 Set Point Mode 5 Set Point Mode 8 Set Point Mode 1 325 degrees 200 degrees 200 degrees 2 350 degrees 300 degrees 250 degrees 3 400 degrees 350 degrees 300 degrees 4 400 degrees 325 degrees 5 500 degrees 350 degrees 6 375 degrees 7 400 degrees 8 425 degrees

Although the above description recites equally sized regions, it is also contemplated that the regions do not need to be equal. For example, if an oven is to be routinely set to a specific temperature(s) one or more regions can be sized to have a larger arcuate distance around potentiometer 116 while the other regions are appropriately decreased in size. In such a three set point mode configuration, a first region and a third region could each be reduced by 25 percent of their otherwise equal ohmic range while the second region could be increased by 50 percent of its otherwise equal ohmic range.

At step 306, the processor 114 determines the resistance range of each individual set point range. For example, if the total resistance of potentiometer 116 is approximately 3000 ohms, and the oven heating circuit 100 is configured for a three set point mode, then each region spans approximately 1000 ohms. At step 308, processor 114 measures that output resistance of potentiometer 116. As shown in FIG. 7, if the shaft 208 of potentiometer 116 is rotated such that the measured resistance in anywhere in the range between greater than approximately 2000 ohms and less than approximately 3000 ohms (e.g. the cross-hatched region shown in FIG. 7), then the processor 114 accesses the temperature setting table and sets the temperature setting signal to the predetermined temperature associated with this third range. Based on the above exemplary table, the temperature setting signal for the configuration of FIG. 7 would be set to 400 degrees. Processor 114 may then cause the oven's heating source to adjust the oven temperature to this temperature setting, which can be monitored with data obtained through probe 118. As the potentiometer's 116 shaft 208 is rotated to a different region, processor 114 may evaluate the new output resistance of the potentiometer 116, determine the temperature setting associated with this new region, and cause the necessary components of the oven to activate or deactivate in order to increment or decrement the oven's temperature, as needed, until the new temperature is achieved.

FIG. 8, illustrates a second exemplary oven heating circuit 800. In oven heating circuit 800, potentiometer 116, processor 114, and probe 118 may operate in similar fashion as previously described. FIG. 8 illustrates the versatility of the disclosed temperature control system, as oven heating circuit 800 illustrates use of the temperature control system in an electric oven that may be powered by either a single-phase or three-phase power source. Although FIGS. 1 and 8 illustrate various general components associated with the respective circuits, these are provided only for exemplary purposes. It is contemplated that more, less, or other components may be used in conjunction with the disclosed temperature control system. 

1. A temperature control system for controlling an oven temperature, comprising: a potentiometer having a shaft and at least a first and a second output terminal, the potentiometer configured to provide a variable resistance between the first and the second output terminal in response to a rotation of the shaft, the variable resistance forming a resistance output signal; and a processor configured to convert the resistance output signal into one of a plurality of discrete temperature settings, where each discrete temperature setting spans a range of resistances of the potentiometer that is less than a full resistance of the potentiometer.
 2. The temperature control system of claim 1, where the plurality of discrete temperature settings comprise three different temperatures.
 3. The temperature control system of claim 1, where the plurality of discrete temperature settings comprises five different temperatures.
 4. The temperature control system of claim 1, where the plurality of discrete temperature settings comprise eight different temperatures.
 5. The temperature control system of claim 1, where the range of resistances comprises three equally sized regions.
 6. The temperature control system of claim 1, where the range of resistances comprises five equally sized regions.
 7. The temperature control system of claim 1, where the range of resistances comprises eight equally sized regions.
 8. The temperature control system of claim 1, where the range of resistances comprises at least one region whose resistance range is larger than another region's resistance range. 